A known drive force transmission apparatus installed in a hybrid vehicle (e.g., a hybrid automobile) is configured to transmit a drive force from a plurality of drive sources to a drive device of the vehicle, which drives the vehicle. For example, JP2012-30775A (corresponding to US2012/0006153A1) teaches a drive force transmission apparatus, which is configured to transmit a drive force of an internal combustion engine and a drive force of a motor to a differential gear of a vehicle through an input shaft and an output shaft.
In the drive force transmission apparatus of JP2012-30775A (corresponding to US2012/0006153A1), the number of clutches is reduced while enabling use of a high gear and a low gear by the internal combustion engine and a first motor in a drive force transmission path to reduce a size of the drive force transmission apparatus. In the drive force transmission apparatus of the first embodiment disclosed in JP2012-30775A (corresponding to US2012/0006153A1), the low gear and the high gear are provided to the input shaft, and an input-side clutch is placed between the low gear and the high gear. Furthermore, in this drive force transmission apparatus, the output shaft is placed parallel to the input shaft, and a first output-side clutch and a second output-side clutch are placed one after another in an axial direction of the output shaft. Furthermore, a driven gear, which is meshed with the high gear, is placed on a differential gear side of the first output-side clutch. In addition, a driven gear, which is meshed with the low gear, is placed on a second motor side of the second output-side clutch. As discussed above, in this drive force transmission apparatus, the clutches and the gears are dispersed along the axial direction of the input shaft and the output shaft. Therefore, the length of the input shaft and the length of the output shaft are disadvantageously increased.
In the drive force transmission apparatus of the second embodiment disclosed in JP2012-30775A (corresponding to US2012/0006153A1), a cylindrical tubular input shaft is placed coaxially with the input shaft on a radially outer side of the input shaft, and the low gear is connected to an engine side of the cylindrical tubular shaft. Furthermore, the input-side clutch is placed on a first motor side of the cylindrical tubular input shaft. With this construction, in comparison to the drive force transmission apparatus of the first embodiment disclosed in JP2012-30775A (corresponding to US2012/0006153A1), the length of the input shaft may be further increased. In addition, a dead volume may possibly be formed between the high gear and the low gear.
As discussed above, in these embodiments of JP2012-30775A (corresponding to US2012/0006153A1), the length of the input shaft and the length of the output shaft are relatively long, so that the installability of the drive force transmission apparatus in the vehicle may possibly be deteriorated. Also, a torsion resistance of the input shaft and the output shaft may possibly be deteriorated.